Multilayer ceramic electronic component manufacturing method

ABSTRACT

A first step of alternately stacking a ceramic sheet and an internal electrode with an adhesive layer between the ceramic sheet and the internal electrode to obtain a laminated body, and a second step of sintering the laminated body are provided. The adhesive layer includes a thermoplastic resin and at least one of Cr, Mg, Al, Si, a Cr compound, an Mg compound, an Al compound, an Si compound and an inorganic powder included in the ceramic sheet. This manufacturing method improves adhesion between a ceramic layer and the internal electrode after sintering and suppresses a structural defect such as delamination or a crack.

TECHNICAL FIELD

[0001] The present invention relates to a method of manufacturing amultilayer ceramic electronic component such as a multilayer ceramiccapacitor.

BACKGROUND ART

[0002]FIG. 7 is a sectional view for illustrating a conventionalmanufacturing process for a multilayer ceramic capacitor.

[0003] First, dielectric material such as barium titanate, an organicbinder and an organic solvent are mixed, and this mixture is used toform ceramic sheet 1 on base film 2 made of, for example, polyethyleneterephthalate (hereinafter referred to as PET). Thereafter, a solutionof synthetic rubber dissolved in an organic solvent is sprayed overceramic sheet 1, thus forming adhesive layer 4. On the other hand, metalfilm 3 in the form of an internal electrode is formed on substrate 5.This metal film 3 is then transferred by pressing substrate 5 formedwith metal film 3 against ceramic sheet 1. Ceramic sheets 1 eachincluding transferred metal film 3 are stacked on top of each other andthen sintered, whereby a sintered body is obtained. Thereafter, thesintered body is provided with external electrodes at its respective endfaces, thus forming the multilayer ceramic capacitor.

[0004] According to the method described above, adhesive layer 4 isformed of only the organic material, and this organic material scattersin sintering, whereby a space is formed, thus causing a structuraldefect such as delamination or a crack.

SUMMARY OF THE INVENTION

[0005] According to the present invention, a method of manufacturing amultilayer ceramic electronic component includes a first step ofalternately stacking a ceramic sheet and an internal electrode with anadhesive layer between the ceramic sheet and the internal electrode toobtain a laminated body, and a second step of sintering the laminatedbody. The adhesive layer includes a thermoplastic resin and at least oneof chromium (Cr), magnesium (Mg), aluminum (Al), silicon (Si), a Crcompound, an Mg compound, an Al compound, an Si compound and aninorganic power included in the ceramic sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIGS. 1-5 are sectional views for illustrating a manufacturingprocess for a multilayer ceramic capacitor in accordance with firstthrough fourth exemplary embodiments of the present invention.

[0007]FIG. 6 is a partially cutaway perspective view of the multilayerceramic capacitor in accordance with the first through fourthembodiments of this invention.

[0008]FIG. 7 is a sectional view for illustrating a conventionalmanufacturing process for a multilayer ceramic capacitor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Exemplary embodiments will be demonstrated hereinafter with amultilayer ceramic capacitor taken as an example. It is to be noted thatsimilar elements in the embodiments have the same reference numerals andwill not be described repeatedly in detail.

First Exemplary Embodiment

[0010] A description will be provided hereinafter of a manufacturingmethod for a multilayer ceramic capacitor in accordance with the firstexemplary embodiment.

[0011] First, slurry is made by mixing dielectric material (inorganicpowder) such as barium titanate with polyvinyl butyral resin as abinder, dibutyl phthalate as a plasticizer and butyl acetate as asolvent. Next, this slurry is applied to separation layer 12 formed onfirst base film 11 by a doctor blade method to form ceramic sheet 13with a thickness of 8 μm, as shown in FIG. 1. Separation layer 12 isprovided to facilitate separation between first base film 11 and ceramicsheet 13 and is made of silicon resin.

[0012] Another slurry is made by mixing one or more kinds of inorganicpowder included in ceramic sheet 13 with polyvinyl butyral resin anddibutyl phthalate so that this slurry has a higher organic materialcontent than ceramic sheet 13. This slurry is applied to a film ofpolyethylene terephthalate (which is not shown and hereinafter referredto as PET film) by the doctor blade method to form sheet-like firstadhesive layer 14. First adhesive layer 14 has an inorganic powdercontent of 50 weight %(wt %) or less, preferably 25 wt % or less (0 wt %is excluded). The thickness of this adhesive layer 14 is 1.0 μm, but thethinner, the more preferable. Thereafter, first adhesive layer 14 istransferred to ceramic sheet 13, and the PET film is removed therefrom.

[0013] On the other hand, second adhesive layer 17 is formed to coverseparation layer 16 with a thickness of about 0.1 to 1.0 μm which isformed on substantially the whole surface of second base film 15, asshown in FIG. 2. Separation layer 16 is formed in the same manner asseparation layer 12, and second adhesive layer 17 is formed in the samemanner as first adhesive layer 14. Next, a metal film, which has auniform thickness of 1.0 μm and is made of nickel (Ni), is formed onsecond adhesive layer 17 by a thin-film forming method such as chemicalvapor deposition(CVD), vacuum evaporation or sputtering. This metal filmformed is made into accurately shaped internal electrode 18 by beingmachined by an excimer laser.

[0014] The PET film is used for first and second base films 11, 15.Since the use of the excimer laser for formation of internal electrode18 eliminates the need to heat the metal film to 200° C. or more, secondbase film 15 serving as a support member remains unaffected. The use ofthe excimer laser can also remove only an unnecessary part of the metalfilm in a short time.

[0015] Next, ceramic sheet 13 with first base film 11 and internalelectrode 18 with second base film 15 are put together as shown in FIG.3 and pressed at 10 MPa by a press (not shown) while being heated at130° C.

[0016] Here, the polyvinyl butyral resin included in ceramic sheet 13and first and second adhesive layers 14, 17 softens, whereby a contactarea between ceramic sheet 13 and internal electrode 18 increases.Adhesion between ceramic sheet 13 and internal electrode 18 is thusinduced, while internal electrode 18 and second adhesive layer 17 areshifted onto first adhesive layer 14. It is essential that the heatingis carried out at such a temperature that the polyvinyl butyral resinincluded in ceramic sheet 13 and first and second adhesive layers 14, 17softens sufficiently without being decomposed. A range of 100° C. to150° C. is thus preferable, and the higher the temperature is in thisrange, the more the adhesive strength improves. To ensure the shift ofinternal electrode 18 and second adhesive layer 17, pressing ispreferably carried out at 10 MPa or more.

[0017] Next, second base film 15 is removed, and consequently, theceramic sheet with the internal electrode, such as shown in FIG. 4, isobtained. Thereafter, the ceramic sheets each including the internalelectrode are so stacked on top of each other in one hundred layers thatceramic sheets 13 and internal electrodes 18 are alternately stacked asshown in FIG. 5 while first base films 11 are removed, whereby alaminated block is obtained. FIG. 5 illustrates the ceramic sheets withthe respective internal electrodes that are stacked in two layers.

[0018] Subsequently, the laminated block is cut into laminated bodies.The laminated body is degreased in an atmosphere of nitrogen at 350° C.in order to prevent internal electrode 18 from oxidizing excessively andthen heated to 1,300° C. to allow ceramic sheets 13 to sinter enough toform ceramic layer 21. This sintering is carried out at a lower oxygenpartial pressure than an equilibrium oxygen partial pressure of Ni toprevent loss of a function of internal electrode 18.

[0019] Thereafter, the laminated body is polished and then formed withexternal electrodes 23 made of copper at its respective end faces whereinternal electrodes 18 are exposed. In this way, the multilayer ceramiccapacitor such as shown in FIG. 6 is obtained.

Second Exemplary Embodiment

[0020] A description will be provided hereinafter of a manufacturingmethod for a multilayer ceramic capacitor in accordance with the secondexemplary embodiment.

[0021] In the present embodiment, paste made by mixing polyvinyl butyralresin, dibutyl phthalate, Al₂O₃ powder and MgO powder is used to makefirst and second adhesive layers 14, 17. The other process steps aresimilar to those in the first exemplary embodiment.

[0022] The total amount of Al₂O₃ powder and MgO powder in each of firstand second adhesive layers 14, 17 accounts for 0.5 to 6.0 wt %,preferably 0.5 to 2.0 wt % of the metal included in internal electrode18.

[0023] When the laminated body is sintered, Al and Mg, which have lowerequilibrium oxygen partial pressure than Ni, remain as oxides at aninterface between ceramic sheet 13 and internal electrode 18, thusimproving adhesion between ceramic sheet 13 and internal electrode 18.

Third Exemplary Embodiment

[0024] A description will be provided hereinafter of a manufacturingmethod for a multilayer ceramic capacitor in accordance with the thirdexemplary embodiment.

[0025] First, ceramic sheet 13 is formed above first base film 11, andfirst adhesive layer 14 formed above a PET film is transferred in thesame manner as in the first exemplary embodiment. First adhesive layer14 is formed of a mixture of polyvinyl butyral resin, dibutyl phthalateand one or more kinds of inorganic powder included in ceramic sheet 13,and this mixture is made to have a higher organic material content thanceramic sheet 13. First adhesive layer 14 has an inorganic powdercontent of 50 wt % or less, preferably 25 wt % or less (0 wt % isexcluded). On the other hand, electrode paste is made by mixing Nipowder with polyvinyl butyral resin as a binder, dibutyl phthalate as aplasticizer and butyl acetate as a solvent. Next, internal electrode 18is formed above a second base film across second adhesive layer 17.Internal electrode 18 is formed by subjecting the electrode paste in amanner of screen-printing.

[0026] Subsequently, the multilayer ceramic capacitor is made in thesame manner as in the first embodiment.

[0027] With this structure, the polyvinyl butyral resin is also includedin internal electrode 18, so that adhesion between ceramic layer 21 andinternal electrode 18 becomes more satisfactory.

Fourth Exemplary Embodiment

[0028] A description will be provided hereinafter of a manufacturingmethod for a multilayer ceramic capacitor in accordance with the fourthexemplary embodiment.

[0029] In the present embodiment, paste made by mixing polyvinyl butyralresin, dibutyl phthalate, Al₂O₃ powder and MgO powder is used to makefirst and second adhesive layers 14, 17. The other process steps aresimilar to those in the third exemplary embodiment.

[0030] The first through fourth embodiments described above can improvethe adhesion between ceramic layer 21 and internal electrode 18 andsuppress a structural defect such as delamination or a crack.

[0031] In the above-described first through fourth embodiments, firstand second adhesive layers 14, 17 are formed to have substantially thesame size as ceramic sheet 13, thereby to cover front and back sides ofinternal electrode 18 entirely. This ensures improved adhesion betweenceramic sheet 13 and internal electrode 18.

[0032] For internal electrode 18, nickel alloy or other metal such ascopper may be used instead of nickel. In cases where internal electrode18 is formed by subjecting the metal film to laser beam machining, useof silver, gold or copper in particular facilitates the machining.

[0033] With first and second adhesive layers 14, 17 each having athickness of more than 0 μm and at most 1.0 μm, a cavity is restrainedfrom forming as a result of the organic material included in theseadhesive layers 14, 17 being burned out. The thickness of each of theselayers 14, 17 is thus preferably reduced as much as possible, butreducing the thickness results in reduced strength, thereby causing hardhandling. Accordingly, the use of polyvinyl butyral resin having aweight average molecular weight of 1,000 or more allows formation ofthin adhesive layers 14, 17 of high strength.

[0034] In formation of the laminated block, the heating carried out atnot less than a softening temperature of the thermoplastic resinincluded in ceramic sheet 13, internal electrode 18 and adhesive layers14, 17 improves fluidity of the resin, thereby improving the adhesionbetween ceramic sheet 13 and internal electrode 18 further. In each ofthe foregoing embodiments, ceramic sheet 13, internal electrode 18, andadhesive layers 14, 17 include the same polyvinyl butyral resin. Theresins, included in them, respectively, thus soften in the same way withheating and become compatible with one another. For this reason, theadhesion between ceramic sheet 13 and internal electrode 18 improvesfurther. Provided that the adhesion between ceramic sheet 13 andinternal electrode 18 can be improved, the thermoplastic resins that areincluded in them, respectively may be of different kinds.

[0035] The method of stacking ceramic sheet 13, first adhesive layer 14,internal electrode 18 and second adhesive layer 17 is not limited tothose described in the foregoing embodiments. Even when the ceramicsheets each including the internal electrode are stacked on top of eachother or even when internal electrodes 18 and ceramic sheets 13 arealternately stacked above a support base, ceramic sheet 13 may be aboveor below internal electrode 18, provided that ceramic sheets 13 andinternal electrodes 18 are stacked with each of first and secondadhesive layers 14, 17 between ceramic sheet 13 and internal electrode18. The presence of the adhesive layer only on one of the sides ofinternal electrode 18 brings about a difference of shrinkage behaviorbetween the top side and the bottom side of internal electrode 18 insintering, whereby the structural defect is easily induced. It is thusnecessary that internal electrode 18 be provided with the adhesive layeron each of its sides. Moreover, it is preferable that first and secondadhesive layers 14, 17 use the same composition for coincidence inshrinkage behavior.

[0036] In the first and third embodiments, at least one kind ofinorganic powder included in ceramic sheet 13, the binder, theplasticizer and the solvent are used to make adhesive layers 14, 17.This is because condition control can be facilitated in themanufacturing process. The use of the inorganic powder included inceramic sheet 13 can restrain a characteristic of ceramic layer 21 fromchanging even when the inorganic powder diffuses into ceramic layer 21during sintering. With the inorganic powder content of 50 wt % or less,preferably 25 wt % or less, the adhesion is secured.

[0037] In the second and fourth embodiments, adhesive layers 14, 17include Al₂O₃ and MgO. The similar advantage can be obtained even whenat least one of Cr, Mg, Al, Si, a Cr compound, an Mg compound, an Alcompound and an Si compound is used. These compounds generally havelower equilibrium oxygen partial pressure than the metal included ininternal electrode 18 of the multilayer ceramic electronic component, sothat these compounds become oxides by the end of sintering of internalelectrode 18, preferably by the time internal electrode 18 starts tosinter, thereby contributing to the adhesion between ceramic sheet 13and internal electrode 18 at the interface between ceramic sheet 13 andinternal electrode 18. The similar advantage can be obtained even whenthe oxide is added from the beginning because the oxide will not bedeoxidized. However, since the metal itself requires enough care inhandling, the compound in the form of oxide, carbonate, acetate ornitrate is preferably used in consideration of productivity.

[0038] These compounds become oxides in sintering and partially diffuseinto ceramic layer 21. To restrain the characteristic change of ceramiclayer 21 as well as to improve the adhesion between ceramic layer 21 andinternal electrode 18, the total amount of metal compound(s) in each ofadhesive layers 14, 17 falls within a proper range. Specifically, thetotal amount of metal compound(s) in the form of oxide(s) accounts for0.5 to 6.0 wt %, preferably 0.5 to 2.0 wt % of the metal included ininternal electrode 18. This amount of metal compound(s) is mixed withthe organic material for formation of desired adhesive layers 14, 17.The addition of Si in the form of glass including Si improveswettability with respect to ceramic sheet 13 and internal electrode 18,thereby allowing further reduction of the thickness of each of adhesivelayers 14, 17 and further suppression of the structural defect.

[0039] The Cr compound, the Mg compound, the Al compound or the Sicompound is preferred to the inorganic powder included in ceramic sheet13 to be included in adhesive layers 14, 17. This is because theadhesion between ceramic sheet 13 and internal electrode 18 improveseasily. Since the inorganic powder sinters after the sintering of Niused for internal electrode 18 ends, while the Cr, Mg, Al and Sicompounds already become oxides by the end of the sintering of Ni,preferably by the time Ni starts to sinter, the Cr, Mg, Al or Sicompound easily performs its function as an adhesive at the interfacebetween ceramic layer 21 and internal electrode 18 during sintering ofNi.

[0040] The metal element included in adhesive layers 14, 17 needs to (1)have a lower equilibrium oxygen partial pressure than the metal includedin internal electrode 18 and (2) oxidize by the end of the sintering ofinternal electrode 18, preferably by the time internal electrode 18starts to sinter so as to lie at the interface between ceramic sheet 13and internal electrode 18.

[0041] The similar advantage can be obtained even when a mixture of theinorganic powder included in ceramic sheet 13 and at least one of theCr, Mg, Al and Si compounds is included in adhesive layers 14, 17. Here,the amount of mixture included not only meets the condition mentionedearlier but also accounts for 50 wt % or less of the adhesive layers.

[0042] Each of the foregoing embodiments has referred to the multilayerceramic capacitor as an example. However, the similar advantage can beobtained by a method of manufacturing a multilayer ceramic electroniccomponent, such as a varistor, an inductor, a ceramic board, athermistor or a piezoelectric ceramic component, which is formed byalternately stacking ceramic layers and internal electrodes.

Industrial Applicability

[0043] A provided manufacturing method for a multilayer ceramicelectronic component according to the present invention suppresses astructural defect resulting from loss of an adhesive layer and providesexcellent adhesion between a ceramic layer and an internal electrode.

Reference Numerals in the Drawings

[0044]1 ceramic sheet

[0045]2 base film

[0046]3 metal film

[0047]4 adhesive layer

[0048]5 substrate

[0049]11 first base film

[0050]12 separation layer

[0051]13 ceramic sheet

[0052]14 first adhesive layer

[0053]15 second base film

[0054]16 separation layer

[0055]17 second adhesive layer

[0056]18 internal electrode

[0057]21 ceramic layer

[0058]23 external electrode

1. A method of manufacturing a multilayer ceramic electronic component,the method comprising the steps of: (A) alternately stacking a ceramicsheet and an internal electrode with an adhesive layer between theceramic sheet and the internal electrode to obtain a laminated body; and(B) sintering the laminated body, wherein the adhesive layer includes athermoplastic resin and at least one of inorganic powders including: (1)Cr, Mg, Al, Si; (2) a Cr compound, an Mg compound, an Al compound, an Sicompound; and (3) a kind of inorganic powder included in the ceramicsheet.
 2. The manufacturing method of claim 1, wherein the adhesivelayer has a size equal to a size of the ceramic sheet.
 3. Themanufacturing method of claim 1, wherein the adhesive layer has a totalinorganic powder content of more than 0 weight % and at most 50 weight%.
 4. The manufacturing method of claim 1, wherein the ceramic sheetincludes a thermoplastic resin similar to the thermoplastic resin of theadhesive layer.
 5. The manufacturing method of claim 1, wherein the step(A) includes heating at not less than a softening temperature of thethermoplastic resin.
 6. The manufacturing method of claim 1, wherein theinternal electrode is formed of a metal film.
 7. The manufacturingmethod of claim 6, wherein the internal electrode is formed of the metalfilm machined with laser beam.
 8. The manufacturing method of claim 1,wherein the adhesive layer has a thickness of more than 0 μm and at most1.0 μm.
 9. The manufacturing method of claim 1, wherein thethermoplastic resin is a butyral resin.